1. Field of the Invention
This invention describes a process for preparing a free flowing finely divided powder of a neutralized sulfonated elastomer and teaches how admixing said powder with other agents such as fillers and oils can lead to free flowing powders capable of being subsequently fabricated into tough elastomeric objects. The neutralized sulfonated elastomeric polymer is converted into a free flowing finely divided powder which does not agglomerate or cold flow under ambient conditions by a variety of processes, preferably by a grinding process conducted at low temperatures. The powder of the neutralized sulfonated elastomeric polymer is blended with at least one chemical additive into a homogeneous mixture, wherein the chemical additive is selected from the group including fillers, polyolefinic thermoplastics, non-polar backbone process oils, lubricants or a metallic oxide and mixtures thereof. The homogeneous mixture is formed into a finished elastomeric article by conventional fabrication.
2. Description of the Prior Art
Historically, in the compounding of extended elastomeric polymer, the elastomeric polymer in a crumb form is mixed with process oils and fillers in an intensive mixing device such as a Banbury. This process requires substantial energy due to the high shear required to mix these viscous polymers. This process has many inherent disadvantages, among which are: the high capital cost of these intensive mixers; the substantial energy input required to mix these materials; the limitations of the types of materials which can be mixed in terms of viscosity; the possibility of scorching or shear degrading the various polymers and chemical additives; and the long mixing times and cycles required for such operations.
Recently, a new class of elastomeric polymers have been developed which are neutralized sulfonated elastomeric polymers. Heretofore, these neutralized sulfonated elastomeric polymers have been compounded in a crumb or diced form with oil and fillers in an intensive mixing device or on a two roll mill.
Ideally, one would like to avoid these previously described mixing operations thereby effecting a substantial economic saving. The process of the present invention describes a process whereby a free flowing finely divided powder of a neutralized sulfonated elastomeric polymer is dry blended with a chemical additive in a suitable mixing device and subsequently formed into a finished elastomeric article by conventional forming processes.
The conventional elastomeric polymers such as ethylene propylene rubbers of useful molecular weight can be formed into a free flowing, finely divided powder, but within a short time at ambient temperature the powder agglomerates into a useless mass because the uncured elastomeric polymer exhibits a tendency to cold flow thereby causing the powder to fuse together into a coalesced mass. This problem can be partially circumvented by going to extremely high molecular weight polymers, but this is not an acceptable approach because such materials still manifest some cold flow, and also they are not useful in many applications because they are too high in molecular weight to be useful. The neutralized sulfonated elastomeric polymers of the present invention do not exhibit this tendency of the polymer to agglomerate into a coalesced mass and will remain as free flowing powders, either alone or when blended with fillers and oils or other chemical additives.
U.S. Pat. No. 3,642,728, herein incorporated by reference, teaches a method of selective sulfonation of olefinic unsaturation sites of an elastomeric polymer to form an acid form of a sulfonated elastomeric polymer. The olefinic sites of the elastomeric polymer are sulfonated by means of a complex of a sulfur trioxide donor and a Lewis base. The SO.sub.3 H groups of the sulfonated elastomer can be readily neutralized with a basic material to form an ionically crosslinked elastomer in the crumb form at room temperature having substantially improved physical properties over an unsulfonated elastomer. However, these sulfonated elastomers, unlike their unsulfonated counterparts, may be processed like a conventional thermoplastic at elevated temperatures under a shear force in an intensive mixing device in the presence of selected preferential plasticizers which dissipate the ionic associations at the elevated temperatures thereby creating a reprocessable elastomer. The basic materials used as neutralizing agents are selected from organic amines or basic materials selected from Groups I, II, III, IV, V, VIB, VIIB and VIII and mixtures thereof of the Periodic Table of Elements.
U.S. Pat. No. 3,836,511, herein incorporated by reference, teaches an improved process for the sulfonation of the olefinic sites of the elastomeric polymer, wherein the improved sulfonating agent is selected from acetyl sulfate, propionyl sulfate and butyryl sulfate. The neutralizing agents employed to neutralize the acid form of the sulfonated elastomeric polymers are organic amines. The resultant ionically crosslinked sulfonated elastomers prepared by this process are isolated in the crumb form.
U.S. Pat. No. 3,870,841, herein incorporated by reference, teaches a method of plasticization of the polymeric backbone of a neutralized sulfonated plastic polymer in a crumb form by means of a polymer chain plasticizer which is a liquid compound having a boiling point of at least about 120.degree. C. The polymer chain plasticizer is selected from a dialkyl phthalate, a process oil or an organic acid ester. Additionally, a domain plasticizer can be incorporated into the composition, wherein the domain plasticizer reversible disrupts the association of the sulfonate groups at a temperature of forming.
U.S. Pat. No. 3,857,854, herein incorporated by reference, teaches a method of improving the processability of neutralized sulfonated elastomeric polymers in the crumb form by the addition of a preferential plasticizer which has at least one functional constituent which exhibits a bond moment whose absolute value is at least about 0.6 Debye, and must be a liquid at the desired processing temperature of the neutralized sulfonated elastomeric polymer.
U.S. patent applications Nos. 542,502 and 524,514, herein incorporated by reference, of the present inventors, filed on Nov. 18, 1974, describe the compounding of a crystalline polyolefinic material with a crumb form of a neutralized sulfonated elastomeric polymer in an intensive mixing device. These aforementioned patents and applications fail to prove a means for the isolation of a free flowing finely divided powder of a neutralized sulfonated elastomeric polymer which can be readily and subsequently dry blended by conventional mixing processes with fillers, oils, thermoplastics, and lubricants into a free flowing, non-agglomerating mixture and the subsequent formation of a finished elastomeric article by conventional fabrication processes.